Method of making magnetic coil casings



May 24, 1932. B. A. ENGHOLM ET AL 1,859,917

METHOD OF MAKING MAGNETIC COIL CASINQS Filed Aug. 16, 1950 gwuemto d Patented 'May 24,. 1932 1 N ED STATES; PATENT OFFICE.

BERNARD A. ENGHOIIM" OF LAKEWOOD, AND JOHN J'- SWENT, OF CLEVELAND, OHIO,

' ASSIGNORS TO THE ROLA COMPANY, OF OAKLAND, GALIFORN'LL'A CORPORATION OF WASHINGTON METHOD OF MAKING MAGNETIC COIL CASINGS Application filed August 16, 1930. Serial No. 475,746.

that ventilation must be providd to dissipate the heat. To obtain the highest magnetic efiiciency however, it is desirable to make the 1 shell cylindrical in form, and'thereby to cause,

uniform distribution of flux density across an interposed moving coil. ccordingly, the practice heretofore of making the shell has been to cut a. disc from a rectangular strip of metal, and then to pass the disc through a series of forming operations until it is sub stantially cup-shaped in form. Thereafter, slots have been milled in the walls of the cup to provide for ventilation of the coil.

This procedure is objectionable for the reason that it entails considerable waste of metal in the formation of the cup from a disc, as the space between the discs on the blank strip become scrap material. Another 2 objection to this procedure is the large number of operations, which must be performed on. the metal before it reaches the final form.

An important object of the present invention is to provide an electro-magnetic shell 80 and a method of making the same, so as to minimize the amount of metaL'which must be scrapped and also the number of operations, which must be performed.

Referring now to the,drawings, Fig. 1 is a side elevation of a loud speaker, which embodies our invention; Fig. 2 is a plan view of a blank form, from which the shell may be made; Fig. 3 is a vertical section through a mould to indicate the position of the blank with reference to the tools at the start of the forming operation; Fig. 4 is a similar view showing the relationship of the tools at another point in the forming operation; Fig. 5 is a section taken on the line 55 in Fig. 4, and Fig. 6 is a perspective view of the shellat the end of the forming operation.

In Fig. 1, we have shown a loud speaker of the cone-type wherein 10 indicates the conical diaphragm, 11 the support which forms'part of the back clamping ring, and 12 the coil shell, which is adapted to be attached to the support 11, as by securing members 13.

To make the shell, we take a rectangular strip of metal 15, as is shown inFig. 2 and place it upon a die 16, as is'shown in Fig. 3. The matrix 17 comprises a cylindrical opening, the diameter of which is less than the width of the blank 15. A punch which coacts with the die is indicated at 18 in Fig. 3, as being disposed above the shell blank. When the punch and die are brought into eoacting relationship, as is shown in Fig. 4, the central portion of the blank forms the bottom 20 of the shell, and the end portions form the side walls 21 and flan es 22. Inasmuch as the width of the blan is less than the length, the side edges 23 of the blank are spaced apart and provide a U-shaped slot 24 in each side of the finished form. Furthermore, by making the diameter of the unch and matrix less than the width of the lank, it isapparent that someof the metal will extend up the side of the shell, thus making the bottom of the slots 24 terminate above the bottom wall 20.

An advantage of the method, which we have devised for making the shell, is that the shell possesses great strength and yet has adequate ventilation space for the coil. A

further advantage is the fact that the entire shell is made by a single forming operation,

and that there is no metal wasted in forming the blank from which the shell is made. We claim:

1. A method of making a shell for an electromagnetic coil, comprising taking a rectangular blank, and deforming it to make a slotted cup-shaped member wherein the original side edges of the blank provide the walls of the slots, and the original end ed es are pressed outwardly to form flanges whlch extend laterally of the cup and wherein the side portions are spaced apart sufliciently far to provide adequate ventilation for the coil.

2. A method of making a shell for an 96 electromagnetic coil, comprising taking a strip of metal, placing it on a die having a cylindrical matrix whose diameter is-less than the width of the blank, aligning the center of the blank with the center of the matrix, 100

and then engaging the'blank with a punch which eoaets with the die matrix so as to form a slotted cup-shaped member in a .singie metal working operation, the relationship tween the width of the blank and the diameter of the matrix being such that the side edges of the shell are spaced apart atthe completion of the forming operation to provide adequate ventilation for the coil.

In witness whereof, we hereunto afiik our signatures.

BERNARD A. ENGHOLM. JOHN J SWENT. 

